1. Field of the Invention
This invention relates to a passive seat belt device, and more particularly to improvements in the driving motor thereof.
2. Description of the Prior Art
There are known two types of passive seat belt device (also called automatic seat belt device), i.e., the two-point type and the three-point type, and in any of these types, a part of webbing is connected to a runner member movable on a rail member. The runner member may be moved on the rail member in response to opening or closing of the door by a driving motor through a driving member such as a geared wire, a tape or the like, whereby the webbing can assume a seat occupant restraining position and a seat occupant liberating position.
In this case, due to the characteristics of the driving motor and the driving member, the sliding resistance of the runner member is variable owing to temperature and generally, the sliding resistance tends to decrease during the time of high temperature and to increase during the time of low temperature. Thus, the runner member moves on the rail member at a relatively high speed during the time of high temperature when the load to the motor may be small, and moves on the rail member at a low speed during the time of low temperature when the load is great. Accordingly, it is not suitable to determine the speed of movement of the runner member, namely, the characteristic of the driving motor, with the time of low temperature or the time of high temperature as a reference, and even if the speed of movement of the runner member is determined with the normal temperature as a reference, the runner member will move at a speed lower than a set value during the time of low temperature and will move at a speed higher than the set value during the time of high temperature. Particularly, under high temperature conditions, if the runner member moves at a high speed, it will collide against the stopper on the rail member at the forward and backward ends of its movement stroke, and the shock resulting therefrom may damage a driving member connecting the motor to the runner member (for example, a geared wire) and the connecting portion driving device thereof (for example, the gear of the motor). Also, under low temperature conditions, the sliding resistance of the runner member may become too great for the runner member to slide well.